U.S. Pat. No. 4,376,228 and U.S. Pat. No. 4,514,581 disclose V-like or U-like troughs solar cells with an ultra thin active semiconductor layer. Lights transmitted through the active layer without being absorbed is reflected out to enter the semiconductor layer at another point where the lights are given another opportunity to be absorbed and converted to electrical energy. U.S. Publication No. 2008/0289684 discloses a high efficiency thin film solar cell using 3-D crystalline silicon (c-Si) film as an absorber layer in conjunction with a plurality of polygonal pyramid-shaped unit cells. The pyramid-shaped structure together with a reflective rear mirror provides a front-side and rear-side light trapping mechanism.
U.S. Pat. No. 4,918,030 describes a light trapping technology employing a pyramid shaped texture at the photovoltaic active silicon level. A metal oxide solution was used to chemically etch the semiconductor surface to create a distribution of pyramids in random orientations and sizes.
The previously disclosed pyramid, V-shaped and U-shaped troughs, however, are not sufficiently effective in light trapping. In particular, these previous designs are not capable of anti-fouling, anti-icing, or self-cleaning.